Presently cellular base stations typically use one receiver per channel and a unique receiver design per mode. Wideband radio receivers capable of multiple channel and multiple modes (e.g. GSM, UMTS, CDMA) represent a promising technology for cellular base stations. However, the application of wideband receiver, otherwise known as software defined radio (SDR), technology to cellular base station design, whilst representing a promising technology for providing low cost multiple channel and multiple mode receivers, has been impeded due to the inability to provide the required dynamic range.
A limitation in applying wideband receiver technology to cellular base station design is that of insufficient dynamic range in the analogue to digital converter (ADC) to cope with interfering signals. The problem is manifest in the simultaneous detection of multiple channel radio signals of multiple modes when interfering signals from one of the modes are at such a level that they block the wanted receive radio frequency band by saturating the analogue to digital converter.
The conventional approach involves the use of switched surface acoustic wave (SAW) filters of varying bandwidths as shown in FIG. 1. By switching the filters, the interfering signal can be taken out of the passband. However, multiple filters and switches increase costs and the use of narrower filters means that wideband reception is not possible.
The problem of dynamic range in wideband multicarrier receivers is discussed in detail in “Receiver dimensioning in a hybrid multicarrier GSM base station”. Harri Posti and Rauli Järvelä. IEE Personal Communications, August 1999. This paper proposes the use of three receivers; a high gain receiver, a low gain receiver and a narrowband receiver to overcome the dynamic range problem.